Ditch Parser Combinators in favour of Parboiled

[theon]

UriParser.scala is currently implemented with core Scala parser combinators. I'd like to replace this with a parboiled implementation as:

• It would remove a couple of ugly workarounds we currently have for a thread safety issue and memory leak issue in Scala parser combinators - see Issue #10 and #11. Both these issues could be removed by using parboiled.
• Parboiled should also give better performance and error reporting with more options for error recovery. See: http://www.decodified.com/parboiled_/2010/08/16/parboiled-for-scala.html